The invention relates generally to vacuum gauges, and more particularly to a vacuum ionization gauge having improved sensitivity.
Nowadays, high vacuum conditions are employed in many technological fields of endeavor, such as in simulation technology in aerospace, superconductor technology, nuclear fusion technology, ultra-low temperature technology, and huge particle accelerator technology. Vacuum gauges for measuring pressure in ultra-high and extremely high vacuum conditions are needed.
When a standard vacuum gauge is used in ultra-high and extremely high vacuum conditions, X-ray and ions produced by means of Electron Stimulated Desorption (ESD) restrict a lowest measuring limit of the vacuum gauge to a relatively low vacuum pressure. In order to extend the lowest measuring limit of the vacuum gauge to a higher vacuum pressure, a vacuum ionization gauge is generally used. As shown in FIG. 3, a typical vacuum ionization gauge 10 includes a grid 12, a modulator 11, a filament 13, a shield 14, an ion reflector 15 and a collector 16. The top of the grid 12 is closed, and the bottom of the grid 12 is open. The modulator 11 is a short wire projecting into a center of the grid 12 from the top of the grid 12. The shield 14 is positioned at the bottom of the grid 12, and has an aperture defined in a center thereof. The ion reflector 15 is generally hemispherical, and is positioned below the shield 14. The collector 16 is a short wire projecting through a small hole in the center of the ion reflector 15.
In use, a zero voltage is applied to the grid 12 by controlling the modulator 11, a negative voltage is applied to the shield 14, and a positive voltage is applied to the ion reflector 15. The filament 13 emits electrons into the grid 12, and the electrons vibrate and collide with gas molecules. Therefore, the gas molecules are ionized to form an ion current. The ions are attracted toward the negative potential shield 14. Most of the ions pass through the aperture of the shield 14, and are focused by the positive potential on the ion reflector 15 onto the collector 16. The vacuum ionization gauge 10 utilizes the shield 14 to turn back most X-rays and ions produced by means of Electron Stimulated Desorption (ESD). Thus a lowest limit of the vacuum ionization gauge 10 can be as little as 10−13 Torr. However, the vacuum ionization gauge 10 has a complex structure, and cannot be advantageously applied in ultra-low temperature technology and huge particle accelerator technology.
Another typical vacuum ionization gauge is shown in FIG. 4. The vacuum ionization gauge 20 includes a metal shield 21, a ceramic column 27, a collector 26, an anode ring 22, and an electron emitting assembly 24. The ceramic column 27 is positioned at one end of the metal shield 21. The electron emitting assembly 24, the anode ring 22 and the collector 26 are positioned on the ceramic column 27 in turn. The electron emitting assembly 24 includes a tungsten filament 241 and a reflector 242. The vacuum ionization gauge 20 is relatively small and simple in structure, and has low power consumption. However, the vacuum ionization gauge 20 cannot turn back most X-rays and ions produced by means of Electron Stimulated Desorption (ESD). This restricts a lowest measuring limit of the vacuum ionization gauge 20 to a relatively low vacuum pressure.
What is needed, therefore, is a vacuum ionization gauge which solves the above-described disadvantages and has improved sensitivity.